ES2800551B2 - Method and apparatus for processing a video signal - Google Patents

Description

DESCRIPTION

Method and apparatus for processing a video signal

technical field

The present invention relates to a method and an apparatus for processing video signals.

prior art

Recently, the demand for high-resolution and high-quality images such as high-definition (HD) images and ultra-high-definition (UHD) images has increased in various application fields. However, image data of higher resolution and quality have increasing amounts of data compared to conventional image data. Therefore, when image data is transmitted using a medium such as conventional broadband and wireless networks, or when image data is stored using a conventional storage medium, transmission and storage costs increase. To solve these problems that occur with an increase in the resolution and quality of the image data, high-efficiency image encoding/decoding techniques can be used.

Image compression technology includes various techniques, including: an inter-prediction technique, for predicting a pixel value included in a current image from an image before or after the current image; an intra-prediction technique of predicting a pixel value included in a current image by using pixel information in the current image; an entropy coding technique of assigning a short code to a value with a high occurrence frequency and assigning a long code to a value with a low occurrence frequency; etc Image data can be effectively compressed using said image compression technology and can be transmitted or stored.

Meanwhile, with the demand for high-resolution images, the demand for stereographic image content, which is a new image service, has also increased. A video compression technique is being discussed to effectively deliver high-resolution and ultra-high-resolution stereographic image content.

Divulgation

technical problem

An object of the present invention is to provide a method and an apparatus for efficiently performing intra-prediction for a target encoding/decoding block in encoding/decoding of a video signal.

An object of the present invention is to provide a method and an apparatus for performing an intra-prediction for a target encoding/decoding block based on a plurality of reference lines.

An object of the present invention is to provide a method and an apparatus for replacing an unavailable reference sample with an available reference sample during generation of a plurality of reference lines in encoding/decoding of a video signal.

An object of the present invention is to provide a method and apparatus for calculating an average value of any one of a plurality of reference lines in encoding/decoding a video signal.

The technical objectives to be achieved by the present invention are not limited to the technical problems mentioned above. Other technical problems that are not mentioned will be immediately understood by those skilled in the art from the following description.

technical solution

A method and apparatus for decoding a video signal according to the present invention can derive a plurality of reference sample lines for a current block, select a reference sample line used for intra-prediction of the current block among the plurality of reference sample lines, and intrapredict for the current block using the selected reference sample line. At this time, if you include a unavailable reference sample in a first reference sample line among the plurality of reference sample lines, the unavailable reference sample is replaced with an available reference sample included in the first or second reference sample line reference sample line different from the first reference sample line.

A method and apparatus for encoding a video signal according to the present invention can derive a plurality of reference sample lines for a current block, select a reference sample line used for intra-prediction of the current block among the plurality of reference sample lines, and intrapredict for the current block using the selected reference sample line. At this time, if an unavailable reference sample is included in a first reference sample line among the plurality of reference sample lines, the unavailable reference sample is replaced with an available reference sample included in the first line. reference sample line or on a second reference sample line different from the first reference sample line.

In the method and apparatus for encoding/decoding a video signal according to the present invention, the unavailable reference sample is replaced with an available reference sample having a shorter distance from the unavailable reference sample between the available reference samples included in the first reference sample line or the second reference sample line.

In the method and apparatus for encoding/decoding a video signal according to the present invention, if a distance between the unavailable reference sample and an available reference sample included in the first reference line is equal to or greater than a threshold value, value not available reference sample is replaced with an available reference sample included in the second reference line.

In the method and apparatus for encoding/decoding a video signal according to the present invention, the second reference line has a larger index value than the first reference line.

In the method and apparatus for encoding/decoding a video signal according to With the present invention, a prediction sample of the current block is generated based on an average value of a part of reference samples included in the selected reference sample line.

In the method and apparatus for encoding/decoding a video signal according to the present invention, a number of reference samples used to calculate the average value among the reference samples included in the selected reference sample line is determined in function of the current block size.

The above briefly summarized features for the present invention are only illustrative aspects of the detailed description of the invention that follows, but do not limit the scope of the invention.

advantageous effects

According to the present invention, efficient intra-prediction can be performed for a target encode/decode block.

According to the present invention, intra-prediction for a target encode/decode block can be performed based on a plurality of reference lines.

In accordance with the present invention, an unavailable reference sample is replaced with an available reference sample during a generation of a plurality of reference lines.

In accordance with the present invention, intra-prediction for a target encoding/decoding block by calculating an average value of one of the plurality of reference lines.

The effects obtainable by the present invention are not limited to the above-mentioned effects, and other effects not mentioned can be clearly understood by those skilled in the art from the following description.

Description of drawings

Fig. 1 is a block diagram illustrating a device for encoding a video according to an embodiment of the present invention;

Fig. 2 is a block diagram of a device for decoding a video according to an embodiment of the present invention;

Fig. 3 is a drawing illustrating an example of hierarchical partitioning of a coding block based on a tree structure according to an embodiment of the present invention.

Fig. 4 is a drawing illustrating a partition mode that can be applied to a coding block when the coding block is interprediction coded.

Fig. 5 is a drawing illustrating kinds of predefined intra-prediction modes for a device for encoding/decoding a video according to an embodiment of the present invention.

Fig. 6 is a diagram illustrating one type of extended intra-prediction modes according to one embodiment of the present invention;

Fig. 7 is a flow chart briefly illustrating an intra-prediction method according to one embodiment of the present invention.

Fig. 8 is a drawing illustrating a method for correcting a prediction sample of a current block based on differential information from neighboring samples according to an embodiment of the present invention.

Figures 9 and 10 are drawings illustrating a method for correcting a prediction sample based on a predetermined correction filter according to an embodiment of the present invention.

Figure 11 shows a range of reference samples for intra-prediction according to an embodiment to which the present invention is applied.

Figures 12 to 14 illustrate an example of filtering on reference samples according to one embodiment of the present invention.

Fig. 15 is a diagram illustrating a plurality of reference sample lines in accordance with one embodiment of the present invention.

Fig. 16 is a flow chart illustrating a method for performing intra-prediction using an extended baseline in accordance with the present invention.

Fig. 17 is a drawing illustrating a plurality of reference lines for a non-square block according to the present invention.

Fig. 18 is a drawing to explain an example where an unavailable reference sample is replaced with an available reference sample located at the shortest distance from the unavailable reference sample.

Figs. 19 and 20 are drawings for explaining an embodiment in which the position of an available reference sample is adaptively determined according to a distance between an unavailable reference sample and an available reference sample included in the same reference line. than the reference sample not available.

Figs. 21 and 22 are drawings illustrating reference samples used to obtain an average value of a reference line according to an embodiment to which the present invention is applied.

mode of invention

A variety of modifications can be made to the present invention and there are various embodiments of the present invention, examples of which will now be given with reference to the drawings and described in detail. However, the present invention is not limited to this, and the exemplary embodiments may be construed as including all modifications, equivalents, or substitutes in a technical concept and technical scope of the present invention. Like reference numerals refer to the like element described in the drawings.

The terms used in the specification, 'first', 'second', etc. can be used to describe various components, but the components must not be construed as limited to the terms. The terms are only used to differentiate a component from other components. For example, the "first" component may be referred to as the "second" component without departing from the scope of the present invention, and the "second" component may also be similarly referred to as the "first" component. The term 'and/or' includes a combination of a plurality of elements or any of a plurality of terms.

It will be understood that where an element is simply referred to as 'connected to' or 'coupled to' another element without being 'directly connected to' or 'directly coupled to' another element in the present description, it may be 'directly' connected to 'or' directly attached to' another element or being connected or attached to another element, with the other element intervening between them. Conversely, when an element is referred to as "directly connected" or "directly coupled" to another feature or element, no intermediate elements are present.

The terms used in the present specification are used merely to describe particular embodiments, and are not intended to limit the present invention. An expression used in the singular encompasses the expression in the plural, unless it has a clearly different meaning in the context. In the present specification, it is to be understood that terms such as "including", "having", etc. are intended to indicate the existence of the features, numbers, stages, actions, elements, parts, or combinations thereof that are described in the specification, and are not intended to exclude the possibility that one or more features, numbers, stages, actions, elements, parts or combinations thereof may exist or be aggregated.

Next, the embodiments of the present invention will be described in detail herein with reference to the accompanying drawings. Hereinafter, the same constituent elements in the drawings are denoted by the same reference numerals, and a repeated description of the same elements will be omitted.

Fig. 1 is a block diagram illustrating a device for encoding a video according to one embodiment of the present invention.

With reference to figure 1, the device 100 for encoding a video may include: an image partitioning module 110, prediction modules 120 and 125, a transformation module 130, a quantization module 135, a reordering module 160, an entropy encoding module 165, an inverse quantization module 140, an inverse transform module 145, a filter module 150, and a memory 155.

The unit as shown in Fig. 1 are shown independently to represent mutually different characteristic functions in the device for encoding a video. Therefore, it does not mean that each constitutional part constitutes a separate hardware or software constitutional unit. In other words, each constitutional part includes each of the constitutional parts listed for convenience. Therefore, at least two constitutional parts of each constitutional part can be combined to form a constitutional part or a constitutional part can be divided into a plurality of constitutional parts to perform each function. The embodiment in which each constitutional part is combined and the embodiment in which one constitutional part is divided are also included in the scope of the present invention, if they do not depart from the gist of the present invention.

Furthermore, some of the constituents may not be essential constituents that perform essential functions of the present invention, but may be selective constituents that only enhance the performance thereof. The present invention can be implemented including only the constitutional parts indispensable to implement the gist of the present invention, except for the constituents used to improve performance. The structure including only the indispensable constituents, except for the selective constituents used for improving performance only, is also included in the scope of the present invention.

The image partitioning module 110 can divide an input image into one or more processing units. Here, the processing unit may be a prediction unit (PU), a transformation unit (TU) or a coding unit (CU). The image partitioning module 110 can divide an image into combinations of multiple encoding units, prediction units, and transformation units, and can encode an image by selecting a combination of encoding units, prediction units, and transformation units. prediction and transformation units with a predetermined criterion (for example, cost function).

For example, an image can be divided into several encoding units. A recursive tree structure, such as a quad tree structure, can be used to divide an image into encoding units. A coding unit that is partitioned into other coding units with an image or a larger coding unit as root may be partitioned with child nodes corresponding to the number of partitioned coding units. An encoding unit that is no longer partitioned by a default constraint serves as a leaf node. That is, when it is assumed that only one square partition is possible for one encoding unit, one encoding unit can be divided into at most four other encoding units.

Hereinafter, in the embodiment of the present invention, the encoding unit may mean a unit that performs encoding, or a unit that performs decoding.

A prediction unit can be one of the partitions partitioned into a square or rectangular shape having the same size in a single coding unit, or a prediction unit can be one of the partitions partitioned to have a different shape/size in a single encoding unit. single coding unit.

When a prediction unit subject to intra-prediction is generated based on a coding unit and the coding unit is not the smallest coding unit, intra-prediction can be performed without splitting the coding unit into multiple NxN prediction units.

The prediction modules 120 and 125 may include an interprediction module 120 that performs the interprediction and an intraprediction module 125 that performs the intraprediction. Whether to perform interprediction or intraprediction for the prediction unit can be determined, and detailed information (for example, an intraprediction mode, a motion vector, a reference image, etc.) can be determined according to each method of prediction. Here, the processing unit subject to prediction may be different from the processing unit. processing for which the prediction method and detailed content are determined. For example, prediction method, prediction mode, etc. they can be determined by the prediction unit, and the transformation unit can perform the prediction. A residual value (residual block) between the generated prediction block and an original block may be input to the transformation module 130. In addition, prediction mode information, motion vector information, etc. used for prediction can be encoded with the residual value by the entropy encoding module 165 and can be transmitted to a device for decoding a video. When a particular coding mode is used, it is possible to transmit to a device for decoding video encoding the original block as it is without generating the prediction block through the prediction modules 120 and 125.

The interprediction module 120 may predict the prediction unit based on the information of at least one of a previous image or a subsequent image of the current image, or may predict the prediction unit based on the information of some coded regions in the image. current, in some cases. The interprediction module 120 may include a reference image interpolation module, a motion prediction module, and a motion compensation module.

The reference image interpolation module may receive reference image information from the memory 155 and may generate pixel information of one integer pixel or less than the integer pixel of the reference image. In the case of luminance pixels, a DCT-based 8-lead interpolation filter with different filter coefficients can be used to generate pixel information of one whole pixel or less than one whole pixel in 1/4 pixel units. In the case of chrominance signals, a DCT-based 4-tap interpolation filter having a different filter coefficient can be used to generate pixel information of one whole pixel or less than one whole pixel in 1/8 units. pixel.

The motion prediction module can perform motion prediction based on the reference image interpolated by the reference image interpolation module. As methods for calculating a motion vector, various methods can be used, such as a full search-based block matching algorithm (FBMA), a three-stage search (TSS), a new three-stage search algorithm (NTS), etc. The motion vector can have a motion vector value in units of 1/2 pixel or 1/4 pixel based on an interpolated pixel. The motion prediction module can predict a current prediction unit by changing the motion prediction method. As motion prediction methods, various methods can be used, such as the skip method, the combination method, the AMVP (Advanced Motion Vector Prediction) method, the intra-block copy method, etc.

The intra-prediction module 125 can generate a prediction unit based on reference pixel information adjacent to a current block that is pixel information in the current image. When the neighbor block of the current prediction unit is an interprediction block and therefore a reference pixel is an interprediction pixel, the reference pixel included in the interprediction block may be replaced by information reference pixels of a neighboring block subject to intraprediction. That is, when a reference pixel is not available, at least one reference pixel of available reference pixels may be used instead of unavailable reference pixel information.

The prediction modes in the intra-prediction may include a directional prediction mode that uses reference pixel information that depends on the direction of the prediction and a non-directional prediction mode that does not use directional information to perform the prediction. A mode for predicting luminance information may be different from a mode for predicting chrominance information, and for predicting chrominance information, intra-prediction mode information used for predicting luminance information or signal information may be used. predicted luminance.

When performing intra-prediction, when the prediction unit size is the same as the transformation unit size, intra-prediction can be performed on the prediction unit based on the pixels to the left, top left, and pixels. above the prediction unit. However, when performing intra-prediction, when the size of the prediction unit is different from the size of the transformation unit, the intra-prediction can be performed using a reference pixel based on the transformation unit. In addition, intraprediction using NxN partitioning can be used only for the unit of smaller encoding.

In the intra-prediction method, a prediction block can be generated after applying an AIS (intra-adaptive filtering) filter to a reference pixel based on the prediction modes. The type of AIS filter applied to the reference pixel may vary. To perform the intra-prediction method, an intra-prediction mode of the current prediction unit can be predicted from the intra-prediction mode of the prediction unit adjacent to the current prediction unit. In prediction of the prediction mode of the current prediction unit by using predicted mode information from the neighboring prediction unit, when the intra-prediction mode of the current prediction unit is the same as the intra-prediction mode of the neighboring unit For the neighbor prediction unit, the information indicating that the prediction modes of the current prediction unit and the neighbor prediction unit are equal to each other may be transmitted using predetermined tagging information. When the prediction mode of the current prediction unit is different from the prediction mode of the neighboring prediction unit, entropy coding may be performed to encode the prediction mode information of the current block.

In addition, a residual block including information on a residual value that is different between the prediction unit under prediction and the original block of the prediction unit can be generated based on the prediction units generated by the prediction modules 120 and 125. The generated residual block can be input into the transformation module 130.

The transformation module 130 can transform the residual block including the residual value information between the original block and the prediction unit generated by the prediction modules 120 and 125 by using a transformation method, such as the discrete transform of cosine (DCT), the discrete sine transform (DST), and KLT. The application of DCT, DST or KLT to transform the residual block can be determined based on the intra-prediction mode information of the prediction unit used to generate the residual block.

The quantization module 135 can quantize the values transformed in a frequency domain by the transformation module 130. The quantization coefficients can vary according to the block or the importance of an image. The Values calculated by the quantization module 135 can be provided to the inverse quantization module 140 and the reordering module 160.

The reordering module 160 may reorder the coefficients of the quantized residuals.

The reordering module 160 can change a coefficient in the form of a two-dimensional block into a coefficient in the form of a one-dimensional vector through a coefficient scan method. For example, the reordering module 160 can scan from a CC coefficient to a coefficient in a high frequency domain using a zigzag scanning method to change the coefficients to be in the form of one-dimensional vectors. Depending on the size of the transformation unit and the intra-prediction mode, scanning in the vertical direction where the coefficients in the form of two-dimensional blocks are scanned in the column direction or scanning in the horizontal direction where the coefficients in the form of two-dimensional blocks are scanned in the direction of the row can be used instead of zigzag scanning. That is, the scanning method among zigzag, vertical-direction scanning, and horizontal-direction scanning can be determined according to the size of the transformation unit and the intra-prediction mode.

The entropy coding module 165 can perform entropy coding based on the values calculated by the reordering module 160. The entropy coding can use various coding methods, for example, Golomb exponential coding, variable length coding Context Adaptive Arithmetic Coding (CABAC) and Context Adaptive Arithmetic Coding (CABAC).

The entropy encoding module 165 can encode a variety of information, such as residual value coefficient information and encoding unit block type information, prediction mode information, partition unit information, data unit information, etc. prediction, transformation unit information, motion vector information, reference frame information, block interpolation information, filtering information, etc. of the reordering module 160 and the prediction modules 120 and 125.

The entropy encoding module 165 can entropy encode the coefficients of the input of the encoding unit of the reordering module 160.

The inverse quantization module 140 can inversely quantize the values quantized by the quantization module 135, and the inverse transformation module 145 can inversely transform the values transformed by the transformation module 130. The residual value generated by the inverse quantization module 140 and the inverse transform module 145 can be combined with the prediction unit predicted by a motion estimation module, a motion compensation module and the intra-prediction module of the prediction modules 120 and 125, so that a block can be generated. rebuilt.

Filter module 150 may include at least one of an unblocking filter, an offset correction unit, and an adaptive loop filter (ALF).

The deblocking filter can remove block distortion that occurs due to boundaries between blocks in the reconstructed image. In determining whether to unlock, the pixels included in multiple rows or columns in the block can be a basis for determining whether to apply the unlock filter to the current block. When the unlock filter is applied to the block, either a strong filter or a weak filter can be applied depending on the strength of unlock filtering required. Furthermore, by applying the unblocking filter, filtering in the horizontal direction and filtering in the vertical direction can be processed in parallel.

The skew correction module can correct skew with the original image in units of one pixel in the image subject to unlocking. To perform displacement correction on a particular image, it is possible to use a method of applying displacement in consideration of the edge information of each pixel or a method of partitioning pixels of an image into the predetermined number of regions, determining a region to be subject to offset, and apply the offset to the given region.

Adaptive Loop Filtering (ALF) can be performed based on the value obtained by comparing the filtered reconstructed image and the original image. The pixels included in the image can be divided into predetermined groups, a filter that will be applied to each of the groups and you can perform an individual filter for each group. Information about whether to apply ALF and a light signal can be transmitted by coding units (CU). The shape and filter coefficient of a filter for ALF can vary depending on each block. Furthermore, the filter for ALF in the same form (fixed form) can be applied regardless of the characteristics of the application's target block.

The memory 155 may store the reconstructed block or the image computed through the filter module 150. The stored reconstructed block or image may be provided to the prediction modules 120 and 125 to perform interprediction.

Fig. 2 is a block diagram of a device for decoding a video according to an embodiment of the present invention.

Referring to Fig. 2, the device 200 for decoding a video may include: an entropy decoding module 210, a reorganization module 215, an inverse quantization module 220, an inverse transformation module 225, prediction modules 230, and 235, a 240 filter module and a 245 memory.

When a video bitstream is input from the device for encoding a video, the input bitstream may be decoded according to a reverse process of the device for encoding a video.

The entropy decoding module 210 can perform entropy decoding according to a reverse entropy encoding process by the entropy encoding module of the device for encoding a video. For example, depending on the methods performed by the device to encode a video, various methods can be applied, such as Golomb exponential coding, context-adapted variable-length coding (CAVLC), and context-adapted binary arithmetic coding (CABAC). .

The entropy decoding module 210 can decode information about intra-prediction and inter-prediction performed by the device to encode a video.

The reordering module 215 can perform entropy reordering of the bit stream decoded by the entropy decoding module 210 in based on the reordering method used on the device to encode a video. The shuffling module can reconstruct and shuffle the coefficients in the form of one-dimensional vectors to the coefficient in the form of two-dimensional blocks. The reordering module 215 can receive information related to the coefficient scan performed on the device for encoding a video and can perform reordering through a method of inverse scan of the coefficients based on the order of scanning performed on the device for encoding. a video.

The inverse quantization module 220 can perform inverse quantization based on a quantization parameter received from the device for encoding a video and the reshuffled coefficients of the block.

The inverse transformation module 225 can perform the inverse transformation, that is, inverse DCT, inverse DST, and inverse KLT, which is the reverse process of the transformation, that is, DCT, DST, and KLT, performed by the transformation module in the quantization result by the device to encode a video. The reverse transformation can be performed based on a transfer unit determined by the device to encode a video. The inverse transformation module 225 of the device for decoding a video can perform transformation schemes selectively (for example, DCT, DST, and KLT) depending on multiple data such as prediction method, current block size, prediction address, etc

The prediction modules 230 and 235 may generate a prediction block based on information about the prediction block generation received from the entropy decoding module 210 and the previously decoded image or block information received from the memory 245.

As described above, just like the operation of the device for encoding a video, when performing intra-prediction, when the size of the prediction unit is the same as the size of the transformation unit, intra-prediction can be performed in unit prediction based on pixels positioned to the left, top left, and top of the prediction unit. When performing intra-prediction, when the size of the prediction unit is different from the size of the transformation unit, intra-prediction can be performed using a reference pixel based on the transformation unit.

Furthermore, intraprediction using NxN partitioning can be used only for the smallest coding unit.

The prediction modules 230 and 235 may include a prediction unit determination module, an interprediction module, and an intraprediction module. The prediction unit determination module can receive a variety of information, such as prediction unit information, prediction mode information of an intra-forecast method, motion prediction information of an inter-forecast method, etc of the entropy decoding module 210, it can divide a stream encode unit into prediction units, and can determine whether inter- or intra-prediction is performed in the prediction unit. By using the information required in the interprediction of the current prediction unit received from the device to encode a video, the interprediction module 230 can perform the interprediction on the current prediction unit based on the information of at least one of a previous image or a subsequent image of the current image including the current prediction unit. Alternatively, the interprediction can be performed based on the information of some previously reconstructed regions in the current image, including the current prediction unit.

To perform interprediction, it can be determined for the coding unit which of a hopping mode, a combining mode, an AMVP mode, and an interblock copy mode is used as the motion prediction method of the prediction unit included in the encoding unit.

The intra-prediction module 235 may generate a prediction block based on the pixel information in the current image. When the prediction unit is a prediction unit subject to intra-prediction, the intra-prediction can be performed based on the information of the intra-prediction mode of the prediction unit received from the device for encoding a video. The intra-prediction module 235 may include an intra-adaptive filtering (AIS) filter, a reference pixel interpolation module, and a CC filter. The AIS filter performs filtering on the reference pixel of the current block, and the application of the filter can be determined according to the prediction mode of the current prediction unit. AIS filtering can be performed on the reference pixel of the current block using the prediction mode of the prediction unit and the AIS filter information received from the device to encode a video. When the prediction mode of the current block is a mode where AIS filtering is not performed, the AIS filter may not be applied.

When the prediction mode of the prediction unit is a prediction mode where intra-prediction is performed based on the pixel value obtained by interpolating the reference pixel, the reference pixel interpolation module can interpolate the reference pixel to generate the reference pixel of an integer pixel or less than an integer pixel. When the prediction mode of the current prediction unit is a prediction mode where a prediction block is generated without interpolation of the reference pixel, the reference pixel cannot be interpolated. The CC filter can generate a prediction block through filtering when the prediction mode of the current block is a CC mode.

The reconstructed block or image may be provided to the filter module 240. The filter module 240 may include the deblocking filter, the offset correction module, and the ALF.

Information about whether or not the unblocking filter is applied to the corresponding block or image and information about which of the strong and weak filters is applied when the unblocking filter is applied can be received from the device for encoding a video. The unblocking filter of the device for decoding a video can receive information about the unblocking filter of the device for encoding a video, and can perform unblocking filtering in the corresponding block.

The offset correction module can perform offset correction on the reconstructed image based on the type of offset correction and offset value information applied to an image when encoding.

The ALF may be applied to the encoding unit based on information whether to apply ALF, ALF coefficient information, etc., received from the device for encoding a video. The ALF information may be provided as being included in a particular parameter set.

Memory 245 may store the reconstructed image or block for use as a reference image or block, and may provide the reconstructed image to an output module.

As described above, in the embodiment of the present invention, for convenience of explanation, the encoding unit is used as a term representing a unit for encoding, but the encoding unit may serve as a unit that performs decoding, as well as coding.

Furthermore, a current block may represent a target block to be encoded/decoded. And, the current block may represent a coding tree block (or a coding tree unit), a coding block (or a coding unit), a transform block (or a transform unit), a prediction (or a prediction unit), or the like, depending on an encoding/decoding step.

An image can be encoded/decoded by being divided into base blocks having a square shape or a non-square shape. At this time, the base block can be referred to as a coding tree unit. The information about whether the coding tree unit has a square or non-square shape or the information about the size of the coding tree unit can be signaled through a set of sequence parameters, a set of parameters image or a split header. The coding tree unit can be divided into a quadtree or a binary tree structure so that a coding unit can be generated.

Fig. 3 is a drawing illustrating an example of hierarchical partitioning of a coding block based on a tree structure according to an embodiment of the present invention.

An input video signal is decoded in predetermined block units. Said predetermined unit for decoding the video input signal is a coding block. The coding block may be a unit that performs intra/interprediction, transformation, and quantization. In addition, a prediction mode (eg, intra-prediction mode or inter-prediction mode) is determined in units of a coding block, and the prediction blocks included in the coding block may share the determined prediction mode. The encoding block may be a square or non-square block having an arbitrary size in the range of 8x8 to 64x64, or it may be a square or non-square block having a size of 128x128, 256x256 or more.

Specifically, the coding block can be hierarchically divided based on at least one of a quad tree and a binary tree. Here, quad-tree based partitioning may mean that one 2Nx2N coding block is divided into four NxN coding blocks, and binary tree-based partitioning may mean that one coding block is divided into two coding blocks. Binary tree-based partitioning can be performed symmetrically or asymmetrically. The coding block divided according to the binary tree may be a square block or a non-square block, such as a rectangular shape. Binary tree based partitioning can be performed in a coding block where quad tree based partitioning is no longer performed. Quad tree based partitioning can no longer be performed on binary tree based partitioned encoding block.

To implement adaptive partitioning based on either the four-tree or binary-tree, the information indicating the four-tree based partitioning, the information about the size/depth of the coding block that enables the four-tree based partitioning, the information indicating partitioning based on binary tree, information about the size/depth of the coding block in which partitioning based on binary tree is allowed, information about the size/depth of the coding block in which partitioning is not allowed binary tree based, information about whether the binary tree based partitioning is performed in a vertical direction or a horizontal direction, etc. can be used.

As shown in Fig. 3, the first coding block 300 with the partition depth (division depth) of k may be divided into multiple second coding blocks based on the fourfold tree. For example, the second coding blocks 310 to 340 can be square blocks that are half the width and half the height of the first coding block, and the partition depth of the second coding block can be increased to k 1 .

The second encoding block 310 with the partition depth of k 1 may be partitioned into multiple third encoding blocks with the partition depth of k 2. The partition of the second encoding block 310 may be perform using selectively one of the quad tree and the binary tree depending on a partition method. Here, the partitioning method can be determined based on at least one of the information indicating the quad-tree based partitioning and the information indicating the binary tree based partitioning.

When the second encoding block 310 is divided based on the quad tree, the second encoding block 310 can be divided into four third encoding blocks 310a that are half the width and half the height of the second encoding block, and the partition depth of the third coding block 310a can be increased to k 2 . In contrast, when the second coding block 310 is divided based on the binary tree, the second coding block 310 can be divided into two third coding blocks. Here, each of the two third coding blocks can be a non-square block having half the width and half the height of the second coding block, and the partition depth can be increased to k 2 . encoding can be determined as a non-square block of a horizontal or vertical direction depending on a partition direction, and the partition direction can be determined based on information whether the binary tree-based partition is performed in a vertical direction or a horizontal direction.

Meanwhile, the second coding block 310 can be determined as a leaf coding block that is no longer partitioned based on the quad-tree or binary-tree. In this case, the leaf encoding block can be used as a prediction block or a transformation block.

Like the partitioning of the second coding block 310, the third coding block 310a may be determined as a leaf coding block, or may be further partitioned based on the quad-tree or binary-tree.

Meanwhile, the third coding block 310b partitioned based on the binary tree can be further divided into coding blocks 310b-2 of a vertical direction or coding blocks 310b-3 of a horizontal direction based on the binary tree, and the partition depth of the relevant coding blocks can be increased to k 3. Alternatively, the third coding block 310b can be determined as a leaf coding block 310b-1 which is no longer partitioned based on the binary tree. In this case, the coding block 310b-1 can be used as a prediction block or a transformation block. However, the above partitioning process can be performed in a limited manner based on at least one of the information about the size/depth of the coding block that allows the quad-tree based partitioning, the information about the size/depth of the block block that allows partitioning based on that binary tree, and information about the size/depth of the encoding block that does not allow partitioning based on binary tree.

A number of a candidate representing a coding block size may be limited to a predetermined number, or a coding block size in a predetermined unit may have a fixed value. As an example, the size of the encoding block in a stream or in an image can be limited to 256x256, 128x128 or 32x32. Information indicating the size of the coding block in the stream or in the image can be signaled via a stream header or an image header.

A coding block is coded using at least one of skip mode, intra-prediction, inter-prediction or skip method. Once a coding block is determined, a prediction block can be determined through the predictive partitioning of the coding block. The predictive partitioning of the coding block can be performed by a partition mode (Part_mode) indicating a partition type of the coding block. A size or a shape of the prediction block can be determined according to the partition mode of the coding block. For example, a prediction block size determined according to the partition mode may be equal to or less than a coding block size.

Fig. 4 is a diagram illustrating a partition mode that can be applied to a coding block when the coding block is interprediction coded.

When a coding block is coded by interprediction, one of 8 partition modes can be applied to the coding block, as in the example shown in Figure 4.

When a coding block is intra-prediction coding, a PART_2Nx2N partition mode or a PART_NxN partition mode may be applied to the coding block.

PART_NxN can be applied when a coding block has a minimum size. Here, the minimum size of the coding block can be predefined in an encoder and a decoder. Or, the information about the minimum size of the coding block can be signaled through a bit stream. For example, the minimum size of the encoding block can be signaled via a segment header, so that the minimum size of the encoding block can be defined per segment.

In general, a prediction block can be from 64^64 to 4x4 in size. However, when an encoding block is encoded by interprediction, the prediction block may be constrained to not be 4x4 in size to reduce memory bandwidth when performing motion compensation.

Fig. 5 is a drawing illustrating kinds of predefined intra-prediction modes for a device for encoding/decoding a video according to an embodiment of the present invention.

The device for encoding/decoding a video can perform intra-prediction using one of the predefined intra-prediction modes. The predefined intra-prediction modes for intra-prediction may include non-directional prediction modes (eg, a flat mode, a DC mode) and 33 directional prediction modes.

Alternatively, to improve the accuracy of the intra-prediction, a greater number of directional prediction modes can be used than the 33 directional prediction modes. That is, M extended directional prediction modes can be defined by subdivision of the angles of the directional prediction modes (M > 33), and a directional prediction mode having a predetermined angle can be derived using at least one of the 33 predefined directional prediction modes.

A greater number of intraprediction modes than 35 intraprediction modes shown in figure 5 can be used. For example, a greater number of intraprediction modes than the 35 intraprediction modes can be used by subdividing the angles of the directional prediction modes or by deriving a directional prediction mode having a predetermined angle using at least one of a predefined number of modes. directional prediction. At this time, the use of a greater number of intra-prediction modes than 35 intra-prediction modes can be referred to as an extended intra-prediction mode.

Fig. 6 shows an example of the extended intra-prediction modes, and the extended intra-prediction modes may include two non-directional prediction modes and 65 extended directional prediction modes. The same numbers of extended intra-prediction modes can be used for a luminance component and a chrominance component, or a different number of intra-prediction modes can be used for each component. For example, 67 extended intra-prediction modes can be used for the luminance component, and 35 intra-prediction modes can be used for the chrominance component.

Alternatively, depending on the chrominance format, a different number of intraprediction modes can be used to perform intraprediction. For example, in the case of the 4:2:0 format, 67 intra-prediction modes can be used for the luminance component to perform intra-prediction, and 35 intra-prediction modes can be used for the chrominance component. In the case of the 4:4:4 format, 67 intra-prediction modes can be used for the luminance component and chrominance component to perform intra-prediction.

Alternatively, depending on the size and/or shape of the block, a different number of intraprediction modes can be used to perform intraprediction. That is, depending on the size and/or shape of the PU or CU, 35 intra-prediction modes or 67 intra-prediction modes can be used to perform intra-prediction. For example, when the CU or PU is smaller than 64x64 or asymmetrically partitioned, 35 intra-prediction modes can be used to perform intra-prediction. When the size of the CU or PU is equal to or greater than 64x64, 67 intra-prediction modes can be used to perform intra-prediction. 65 directional intraprediction modes can be allowed for Intra_2Nx2N, and only 35 directional intraprediction modes can be allowed for Intra_NxN.

The size of a block to which the extended intraprediction mode is applied can be configured differently for each sequence, image, or segment. For example, the extended intra-prediction mode is set to apply to a block (eg, CU or PU) that is larger than 64x64 in size at the first split. On the other hand, it is established that the extended intraprediction mode is applied to a block that has a size greater than 32x32 in the second division. The information representing the size of a block to which the extended intra-prediction mode is applied may be signaled in units of a sequence, a picture, or a slice. For example, the information indicating the size of the block to which the extended intraprediction mode applies can be defined as 'log2_extended_intra_mode_size_minus4' obtained by taking a logarithm of the block size and then subtracting the integer 4. For example, if a value of log2_extended_intra_mode_size_minus4 is 0, it can indicate that the extended intraprediction mode can be applied to a block that is equal to or greater than 16x16 in size. And if a value of log2_extended_intra_mode_size_minus4 is 1, it can indicate that the extended intraprediction mode can be applied to a block that is equal to or greater than 32x32 in size.

As described above, the number of intra-prediction modes can be determined by considering at least one of a color component, a chrominance format, and a size or shape of a block. In addition, the number of intra-prediction mode candidates (for example, the number of MPMs) used to determine an intra-prediction mode of a current block for encoding/decoding may also be determined according to at least one of a color component. , a color format, and the size or shape of a block. With the drawings, a method for determining an intra-prediction mode of a current block to encode/decode and a method for performing intra-prediction using the determined intra-prediction mode will be described.

Fig. 7 is a flow chart briefly illustrating an intra-prediction method according to one embodiment of the present invention.

Referring to Fig. 7, an intra-prediction mode of the current block can be determined in step S800.

Specifically, the intra-prediction mode of the current block can be derived based on a candidate list and an index. Here, the candidate list contains multiple candidates, and the multiple candidates may be determined based on an intra-prediction mode of the neighbor block adjacent to the current block. The neighbor block can include at least one of the blocks located on the top, bottom, left, right, and corner of the current block. The index can specify one of multiple candidates from the candidate list. The candidate specified by the index may be set to the intra-prediction mode of the current block.

An intra-prediction mode used for intra-prediction in the neighboring block may be set as a candidate. In addition, an intra-prediction mode having directionality similar to that of the intra-prediction mode of the neighboring block may be set as a candidate. Here, the intra-prediction mode having a similar directionality can be determined by adding or subtracting a predetermined constant value to or from the neighboring block's intra-prediction mode. The default constant value can be an integer, such as one, two, or more.

The candidate list may further include a predetermined mode. The default mode may include at least one of a planar mode, a DC mode, a vertical mode, and a horizontal mode. The default mode can be adaptively added by considering the maximum number of candidates that can be included in the candidate list of the current block.

The maximum number of candidates that can be included in the candidate list can be three, four, five, six or more. The maximum number of candidates that can be included in the candidate list may be a preset value in the device for encoding/decoding a video, or may be variably determined based on a characteristic of the current block. The feature can mean the location/size/shape of the block, the number/type of intraprediction modes the block can use, a color type, a color format, etc. Alternatively, the information indicating the maximum number of candidates that can be included in the candidate list can be indicated separately, and the maximum number of candidates that can be included in the candidate list can be variably determined using the information. The information indicating the maximum number of candidates may be indicated at at least one of a sequence level, an image level, a division level and a block level.

When the extended intraprediction modes and the predefined intraprediction modes are used selectively, the intraprediction modes of neighboring blocks can be transformed into indices corresponding to the extended intraprediction modes, or to indices corresponding to the 35 intraprediction modes, by which Candidates can be referred. For transformation to an index, a predefined table can be used, or a scale operation based on a default value can be used. Here, the predefined table may define an allocation relationship between different intra-prediction mode groups (eg, extended intra-prediction modes and intra-prediction 35 modes).

For example, when the left neighbor block uses all 35 intra-prediction modes and the intra-prediction mode of the left neighbor block is 10 (a horizontal mode), it can be transformed to an index of 16 corresponding to a horizontal mode in the extended intra-prediction modes.

Alternatively, when the upper neighbor block uses the extended intraprediction modes and the intraprediction mode the upper neighbor block has an index of 50 (a vertical mode), it can be transformed to an index of 26 corresponding to a vertical mode in all 35 modes. of intraprediction.

According to the method described above for determining the intra-prediction mode, the intra-prediction mode can be derived independently for each component of the luminance and the chrominance component, or the intra-prediction mode of the chrominance component can be derived depending on the intra-prediction mode of the luminance component. luminance.

Specifically, the intra-prediction mode of the chrominance component can be determined based on the intra-prediction mode of the luminance component as shown in the following Table 1.

Table 1

In Table 1, intra_chroma_pred_mode means signaled information for specifying the intra-prediction mode of the chrominance component, and IntraPredModeY indicates the intra-prediction mode of the luminance component.

Referring to Fig. 7, a reference sample for intra-prediction of the current block can be derived in step S710.

Specifically, a reference sample for intra-prediction can be derived based on a neighboring sample of the current block. The neighbor sample may be a reconstructed sample from the neighbor block, and the reconstructed sample may be a reconstructed sample before a loop filter is applied or a reconstructed sample after the loop filter is applied.

A neighbor sample reconstructed before the current block can be used as the reference sample, and a neighbor sample filtered based on a predetermined intra filter can be used as the reference sample. Filtering neighboring samples using an intra filter can also be called reference sample filtering. The intra filter may include at least one of the first intra filter applied to multiple adjacent samples located on the same horizontal line and the second intra filter applied to multiple neighboring samples located on the same vertical line. Depending on the positions of the neighboring samples, one of the first intra filter and the second intra filter can be applied selectively, or both intra filters can be applied. At this time, at least one filter coefficient of the first intra filter or the second intra filter may be (1, 2, 1), but is not limited thereto.

The filtering may be performed adaptively based on at least one of the intraprediction modes of the current block and the size of the transform block for the current block. For example, when the intraprediction mode of the current block is CC mode, Vertical mode, or Horizontal mode, filtering may not be performed. When the block size of transformation is NxM, filtering cannot be performed. Here, N and M can be the same or different values, or they can be values of 4, 8, 16, or more. For example, if the transform block size is 4x4, filtering cannot be performed. Alternatively, filtering can be performed selectively based on the result of a comparison of a predefined threshold and the difference between the intraprediction mode of the current block and the vertical mode (or horizontal mode). For example, when the difference between the intraprediction mode of the current block and the vertical mode is greater than a threshold, filtering can be performed. The threshold can be defined for each transform block size as shown in Table 2.

Table 2

The intra filter can be determined as one of multiple intra filter candidates predefined in the device for encoding/decoding a video. For this purpose, an index can be pointed out that specifies an intra filter of the current block among the multiple intra filter candidates. Alternatively, the intra filter can be determined based on at least one of the current block size/shapes, the transform block size/shapes, filter strength information, and neighboring sample variances.

Referring to Fig. 7, intra-prediction can be performed using the intra-prediction mode of the current block and the reference sample in step S720.

That is, the prediction sample of the current block can be obtained using the intra-prediction mode determined in step S700 and the reference sample derived in step S710. However, in the case of intra-prediction, a bounding sample of the neighboring block may be used, and therefore the quality of the prediction image may decrease. Therefore, a correction process can be performed on the prediction sample generated through the prediction process described above, and it will be described in detail with reference to Figs. 8 to 10. However, the correction process is not limited to to be applied only to the intraprediction sample, and can be applied to an interprediction sample or the sample reconstructed.

Fig. 8 is a drawing illustrating a method for correcting a prediction sample of a current block based on differential information from neighboring samples according to an embodiment of the present invention.

The current block prediction sample may be corrected based on the differential information of multiple neighboring samples for the current block. The correction can be performed on all prediction samples in the current block, or it can be performed on prediction samples in predetermined partial regions. The partial regions may be one row/column or multiple rows/columns, and these may be regions preset for correction in the device for encoding/decoding a video. For example, the correction may be performed on a row/column located at a current block boundary or may be performed on a plurality of rows/columns from a current block boundary. Alternatively, the partial regions may be variably determined based on at least one of the current block size/shape and the intra-prediction mode.

Neighboring samples can belong to neighboring blocks located in the upper left and upper left corner of the current block. The number of neighboring samples used for the correction can be two, three, four or more. The positions of the neighboring samples can be variably determined depending on the position of the prediction sample that is the correction target in the current block. Alternatively, some of the neighboring samples may have fixed positions regardless of the position of the prediction sample that is the target of correction, and the remaining neighbor samples may have variable positions depending on the position of the prediction sample that is the target of correction. correction.

Differential information from neighboring samples may mean a differential sample between neighboring samples, or it may mean a value obtained by scaling the differential sample by a predetermined constant value (eg, one, two, three, etc.). Here, the default constant value can be determined by considering the position of the prediction sample that is the correction target, the position of the column or row that includes the prediction sample that is the correction target, the position of the sample of prediction within the column or row, etc.

For example, when the intraprediction mode of the current block is the vertical mode, the differential samples between the upper left neighbor sample p(-1, -1) and the neighboring samples p(-1, y) adjacent to the left boundary of the block current can be used to obtain the final prediction sample as shown in Equation 1.

equation 1

P ( 0,y) = P(0,y)+((p(-1,y)-p(-1,-1)) >> 1 for y = 0...N-1

For example, when the intraprediction mode of the current block is the horizontal mode, the differential samples between the upper left neighbor sample p(-1, -1) and the neighboring samples p(x, -1) adjacent to the upper block boundary current can be used to obtain the final prediction sample as shown in Equation 2.

equation 2

P(x,0) = P(x,0)+((p(x,-1)-p(-1,-1)) >> 1 for x = 0...N-1

For example, when the intraprediction mode of the current block is the vertical mode, the differential samples between the upper left neighbor sample p(-1, -1) and the neighboring samples p(-1, y) adjacent to the left boundary of the block current can be used to get the final prediction sample. Here, the differential sample can be added to the prediction sample, or the differential sample can be scaled by a default constant value, and then added to the prediction sample. The default constant value used in scaling can be determined differently depending on the column and/or row. For example, the prediction sample can be corrected as shown in Equation 3 and Equation 4.

Equation 3

P(0,y) = P(0,y)+((p(-1,y)-p(-1,-1)) >> 1 for y = 0...N-1

Equation 4

P ( 1,y) = P(0,y)+((p(-1,y)-p(-1,-1)) >> 2 for y = 0...N-1

For example, when the intraprediction mode of the current block is the horizontal mode, the differential samples between the upper left neighbor sample p(-1, -1) and the neighboring samples p(x, -1) adjacent to the upper block boundary current can be used to get the final prediction sample, as described in the case of vertical mode. For example, the prediction sample can be corrected as shown in Equation 5 and Equation 6.

equation 5

P(x,0) = P(x,0)+((p(x,-1)-p(-1,-1)) >> 1 for x = 0...N-1

Equation 6

P(x,1) = P(x,1)+((p(x,-1)-p(-1,-1)) >> 2 for x = 0...N-1

Figures 9 and 10 are drawings illustrating a method for correcting a prediction sample based on a predetermined correction filter according to an embodiment of the present invention.

The prediction sample may be corrected based on the neighbor sample of the prediction sample that is the correction target and a predetermined correction filter. Here, the neighbor sample may be specified by an angular line of the directional prediction mode of the current block, or it may be at least one sample placed on the same angular line as the prediction sample that is the correction target. In addition, the neighbor sample may be a prediction sample in the current block, or it may be a reconstructed sample in a neighbor block reconstructed before the current block.

At least one of the lead numbers, the intensity, and a filter coefficient of the correction filter may be determined based on at least one of the positions of the prediction sample that is the correction target, regardless of whether the lead sample prediction is the target of the correction is placed at the current block boundary, the block intra-prediction mode current, the angle of the directional prediction mode, the prediction mode (inter or intra mode) of the neighboring block, and the size/shape of the current block.

Referring to Figure 9, when the directional prediction mode has an index of 2 or 34, at least one prediction/reconstructed sample placed at the bottom left of the prediction sample that is the correction target and the reconstructed sample default correction can be used to obtain the final prediction sample. Here, the prediction/reconstructed sample at the bottom left may belong to a line prior to a line that includes the prediction sample that is the correction target. The prediction/reconstructed sample at the bottom left can belong to the same block as the current sample, or to the neighboring block adjacent to the current block.

Filtering for the prediction sample can be performed only on the line located at the block boundary, or it can be performed on multiple lines. The correction filter can be used where at least one of the number of filter taps and a filter coefficient is different for each of the lines. For example, you can use a filter (1/2, 1/2) for the first line left closest to the block boundary, you can use a filter (12/16, 4/16) for the second line, you can use a filter (14/16, 2/16) for the third line, and you can use a filter (15/16, 1/16) for the fourth line.

Alternatively, when the directional prediction mode has an index of 3 to 6 or 30 to 33, filtering can be done at the block boundary as shown in Figure 10, and a 3-tap correction filter can be used. to correct the prediction sample. Filtering can be done using the bottom left sample of the prediction sample, which is the correction target, the bottom sample of the bottom left sample, and a 3-lead correction filter that takes the target sample as input. prediction that is the target of correction. The position of the neighboring sample used by the correction filter can be determined differently depending on the directional prediction mode. The filter coefficient of the correction filter can be determined differently depending on the directional prediction mode.

Different correction filters can be applied depending on whether the neighboring block is coded in the inter mode or the intra mode. When the neighboring block is coded in the intra mode, a filtering method can be used where gives more weight to the prediction sample, compared to when the neighbor block is coded in inter mode. For example, in the case that the intra-prediction mode is 34, when the neighbor block is coded in the inter mode, a filter (1/2, 1/2) can be used, and when the neighbor block is coded in the intra mode, a filter (4/16, 12/16) can be used.

The number of lines to filter in the current block may vary depending on the size/shape of the current block (eg, the encoding block or the prediction block). For example, when the current block size is equal to or less than 32x32, filtering can be done on a single line at the block boundary; otherwise, filtering can be done on multiple lines, including a line at the block boundary.

Figures 9 and 10 are based on the case where the intra-prediction modes in Figure 4 are used, but the same or similar can be applied to the case where the extended intra-prediction modes are used.

Figure 11 shows a range of reference samples for intra-prediction according to an embodiment to which the present invention is applied.

Referring to Figure 11, intra-prediction can be performed using the reference samples P(-1, -1), P(-1, y) (0 <= y <= 2N-1) and P(x, -1 ) (0 <= x <= 2N-1) located at a boundary of a current block. At this time, filtering on reference samples is performed selectively based on at least one of an intraprediction mode (for example, intraprediction mode index, directionality, angle, etc.) of the current block or the size of the intraprediction mode. a transform block related to the current block.

Filtering on reference samples can be performed using a predefined intra filter on an encoder and decoder. For example, an intra filter with a filter coefficient of (1,2,1) or an intra filter with a filter coefficient of (2,3,6,3,2) can be used to obtain final reference samples for its use in intraprediction.

Alternatively, at least one of a plurality of intra filter candidates may be selected to perform filtering on reference samples. In this case, the plurality of intra filter candidates may differ from each other in at least one of a filter strength, a filter coefficient, or a tap number (eg, a number of filter coefficients, a filter length). A plurality of intra filter candidates may be defined at at least one of a sequence, image, slice or block level. That is, a sequence, an image, a segment or a block where the current block is included can use the same plurality of intra filter candidates.

Hereinafter, for convenience of explanation, it is assumed that a plurality of intra-filter candidates includes a first intra-filter and a second intra-filter. It is also assumed that the first intra filter is a 3-lead filter (1,2,1) and the second intra filter is a 5-lead filter (2,3,6,3,2).

When the reference samples are filtered by applying a first intra filter, the filtered reference samples can be derived as shown in Equation 7.

Equation 7

P ( - 1 1 ) = ( P ( - 1,0 )+ 2 P ( - 1 1 ) P ( 0 , - 1 ) 2 ) » 2

P ( - 1 ,y )= ( P ( - 1,J, 1 ) 2 P ( - 1 ,y )+ p ( - l ,y - l ) 2 ) » 2

P ( x,~ 1 ) = ( PO 1 1 ) 2 PO , - 1 ) P ( x - 11 ) 2 ) » 2

When the reference samples are filtered by applying the second intra filter, the filtered reference samples can be derived as shown in the following equation 8.

Equation 8

PC - 1 1 )= (2 P ( -2 ,0 )+ 3 P ( - 1,0 ) 6 P ( - 1 1 ) 3 P ( 0 , - 1 ) 2 P ( 0 , - 2 ) 8 ) » 4

PC - 1,> 0 = (2 P ( - l ,y 2 ) 3 P ( -1 , y + 1 ) 6 P ( - l , y ) 3 P ( - l , y - 1 )+ 2P ( - 1 , y - 2 ) 8 ) » 4 P ( x - 1 ) = ( 2 PO 2 , - 1 ) 3 PO 1,-1 ) 6 P ( x - 1 ) 3 P ( x - 11 ) 2 P ( x - 2 - 1 ) 8 ) » 4

In Equations 7 and 8 above, x can be an integer between 0 and 2N-2, and y can be an integer between 0 and 2N-2.

Alternatively, depending on the position of a reference sample, you can determining one of a plurality of intra filter candidates, and filtering on the reference sample can be performed using the determined one. For example, a first intra filter may be applied to reference samples included in a first range, and a second intra filter may be applied to reference samples included in a second range. Here, the first rank and the second rank can be distinguished based on whether they are adjacent to a boundary of a current block, whether they are located on the top or left side of a current block, or whether they are adjacent to a corner of a current block. For example, as shown in Figure 12, filtering on reference samples (P(-1, -1), P(-1,0), P(-1,1), ... , P(-1 , N-1) and P(0, -1), P(1, -1), ...) that are adjacent to a boundary of the current block is performed by applying a first intra filter as shown in Equation 7, and filtering on the other reference samples that are not adjacent to a current block boundary is performed by applying a second reference filter as shown in Equation 8. It is possible to select one of a plurality of candidates within the filter based on the type of transformation used for a current block, and perform filtering on reference samples using the selected one. Here, the type of transformation can mean (1) a transformation scheme such as DCT, DST, or KLT, (2) a transformation mode indicator such as a 2D transformation, a 1D transformation, or no transformation, or (3) the number of transformations such as a first transform and a second transform. Hereinafter, for convenience of description, the transformation type is assumed to mean the transformation scheme such as DCT, DST and KLT.

For example, if a current block is encoded using a DCT, filtering may be performed using a first intra-filter, and if a current block is encoded using a DST, filtering may be performed using a second intra-filter. Or, if a current block is encoded using DCT or DST, filtering may be performed using a first intra-filter, and if the current block is encoded using a KLT, filtering may be performed using a second intra-filter.

Filtering can be performed using a selected filter based on a transformation type of a current block and a position of a reference sample. For example, if a current block is encoded using a DCT, filtering on the reference samples P(-1, -1), P(-1,0), P(-1,1)___P(-1, N- 1) and P(0, -1), P(1, -1), ... , P(N-1, -1) can be performed using a first intra filter, and filtering on other reference samples is can be done using a second intra filter. If a current block is encoded using a DST, filtering on the reference samples P(-1, -1), P(-1,0), P(-1,1), ... , P(-1, N- 1) and P(0, -1), P(1, -1), ... , P(N-1, -1) can be performed using a second intra filter, and filtering on other reference samples can be can be done using a first intra filter.

One of a plurality of intra filter candidates can be selected based on whether a transformation type of a neighboring block including a reference sample is the same as a transformation type of a current block, and filtering can be performed using the selected intrafilter candidate. For example, when a current block and a neighbor block use the same transformation type, filtering is performed using a first intra filter, and when the transformation types of a current block and a neighbor block are different from each other, the second intra filter can be used to perform filtering.

It is possible to select any of a plurality of intra filter candidates based on the transformation type of a neighboring block and perform filtering on a reference sample using the selected one. That is, a specific filter can be selected considering a type of transformation of a block where a reference sample is included. For example, as shown in Figure 13, if a block adjacent to the left/bottom left of a current block is a block encoded using a DCT, and a block adjacent to the top/top right of a block is a block encoded using a DST, filtering adjacent reference samples to the left/bottom left of a current block is done by applying a first intra filter and filtering on the reference samples adjacent to the top/bottom left of a current block. top right of a current block is done by applying a second intra filter.

In units of a default region, a usable filter can be defined in the corresponding region. Here, the unit of the default region can be any of a sequence, an image, a sector, a group of blocks (for example, a row of encoding tree units), or a block (for example, an encoding tree unit). encoding) or, another region can be defined that shares one or more filters. A reference sample can be filtered using a filter assigned to a region in which a current block is included.

For example, as shown in Figure 14, it is possible to perform filtering on reference samples using different filters in CTU units. In this case, information indicating whether the same filter is used in a sequence or in an image, a type of filter used for each CTU, an index specifying a filter used in the corresponding CTU among the available intra filter candidates can be be signaled by a Sequence Parameter Set (SPS) or a Picture Parameter Set (PPS).

The intra filter described above can be applied in units of one coding unit. For example, filtering can be performed by applying a first intra-filter or a second intra-filter to refer to samples around a coding unit.

When an intra-prediction mode of a current block is determined, the intra-prediction can be performed using a reference sample adjacent to the current block. For example, the prediction samples of a current block can be generated by averaging reference samples, or they can be generated by duplicating reference samples in a specific direction considering a directionality of an intra-prediction mode. As described above in an example referring to Figure 11, P(-1, -1), P(-1, y) (0 <= y <= 2N-1), P(x, -1) (0 <= x <= 2N-1) that are located on the boundary of a current block can be used as reference samples.

When a sample included in a neighboring block adjacent to a current block is determined to be unavailable as a reference sample, the unavailable sample may be replaced with an available reference sample. For example, a neighboring sample may be determined to be unavailable in the case that a position of a sample included in a neighboring block is outside of an image, a sample included in a neighboring block is present in a different portion of a current block, or a sample included in a neighboring block is included in a coded block using an intra-prediction. Here, if a sample included in a prediction-coded block is not available, it can be determined based on information indicating whether a sample included in a prediction-coded block should be used as a reference sample when performing a prediction. intraprediction of a current block. In this case, the information may be a 1-bit flag (eg 'restricta_intra_prediction_flag'), but is not limited to that. For example, when a value of 'restricta_intra_prediction_flag' is 1, it can be determined that a sample included in a block coded by a prediction is not available as a reference sample. Hereinafter, a sample that cannot be used as a reference sample will be called a non-available reference sample.

In the example shown in Figure 11, when a lower left sample (for example, P(-1, 2N-1)) is determined to be unavailable, the lower left sample can be replaced with a first available reference sample that first seeks to scan the available samples in a predetermined order. Here, the scan order can be performed sequentially from an adjacent sample to the lower left sample. For example, in the example shown in Figure 11, when a sample P(-1, 2N-1) is not available, the scan can be performed in an order from P(-1, -2N-2) to P(- 1, -1), P(-1) to P(2N-1, -1). P(-1, 2N-1) can be replaced with a first available reference sample found as a result of the scan.

When a left reference sample, except a reference sample located in the lower left corner is not available, the left reference sample may be replaced with a reference sample adjacent to a lower part of the left reference sample. For example, an unavailable reference sample P(-1, y) between P(-1, 2N-1) and P(-1, -1) can be replaced with a reference sample P(-1, y 1) .

When an upper reference sample is not available, the upper reference sample can be replaced with an adjacent reference sample to the left of the upper reference sample. For example, an unavailable reference sample P(x, -1) between P(0, -1) and P(2N-1, -1) can be replaced with a reference sample P(x-1, -1) .

A set of reference samples for a current block may be called a "reference line" (or "intrareference line" or "reference sample line"). Here, the reference line may include a set of reference samples made up of one row and one column. For example, in the example shown in Figure 11, a 'reference line' is a set of reference samples including P(-1, 2N-1) to P(-1, 1), P(0, -1 ) to P(2N-2, -1). An intraprediction of a current block can be made based on the samples of reference included in a reference line. An intra-prediction of a current block, using reference samples included in a reference line, may be performed based on an intra-prediction mode of a current block, for example, when an intra-prediction mode of a current block is a CC mode, a prediction signal can be generated using a weighted prediction and average of the reference samples included in the reference line. For example, when an intra-prediction mode of a current block is a CC mode, prediction samples of the current block can be obtained according to Equation 9.

Equation 9

In Equation 9, dcVal can be generated based on an average value of samples, except P(-1, -1) among the reference samples included in a reference line.

A flat mode provides effective prediction efficiency in a smooth area that does not have strong edges, and is effective for improving block boundary discontinuity or image quality deterioration of a block boundary. When an intraprediction mode of a current block is a flat mode, an interim prediction sample in the horizontal direction of the current block can be obtained by using a reference sample adjacent to an upper right corner of the current block and a reference sample having a coordinate and identical to the provisional prediction sample in the horizontal direction, and a provisional prediction sample in the vertical direction of the current block can be obtained by using a reference sample adjacent to a lower left corner of the current block and a reference sample with a coordinate x identical to the interim forecast sample in the vertical direction. For example, one provisional prediction sample in the horizontal direction and one provisional prediction sample in the vertical direction can be obtained from a current block according to Equation 10.

quack n

Ph(x,y) = ( N - l - x ) *P(—l,y) ( x 1 ) * P(N, —1)

P ¹⁷ (x,y) = (N — 1 — y) * P ( x , - l ) ( y 1 ) * P(-1,N)

A prediction sample of a current block can be generated by adding an interim prediction sample in the horizontal direction and an interim prediction sample in the vertical direction, and then changing the sum result to a given value according to the size of a block current. For example, a prediction sample of a current block can be obtained according to Equation 11.

Equation 11

P(x,y) = (Ph(x,y) Pv(x,y) N ) » ( log2{N ) 1)

An intra-prediction of a current block can be performed using a plurality of reference lines. Assuming that a current block has size WxH, the kth reference line can include p(-k, -k), reference samples located in a row identical to p(-k, -k) (for example, samples of reference from p( k 1, -k) to p(W H 2 (k-1), -k) or reference samples from p(-k 1, -k) to p(2W 2 (k-1), -k) ) and reference samples located in a column identical to p(-k, -k) (for example, reference samples from p(-k, -k 1) to p(-k, W H 2 (k -1)) or samples from p(-k, -k 1) to p(-k, 2H 2 (k-1))).

Fig. 15 exemplifies a plurality of reference sample lines. As in the example shown in Fig. 15, when a first reference line adjacent to a boundary of a current block is called "reference line 0", the kth reference line may be set adjacent to reference line (k -1)-th.

Alternatively, unlike the example shown in Figure 15, it is also possible to set all reference lines to have the same number of reference samples.

An intra-prediction of a current block can be made by at least one of a plurality of reference lines. A method for performing an intraprediction using a plurality of baselines as described above may be referred to as the "intra-forecast method using an extended reference sample" or the "extended intra-forecast method". In addition, a plurality of reference lines may be referred to as an 'extended reference line'.

Whether or not to perform intra-prediction using an extended reference line can be determined based on the information signaled via a bit stream. Here, the information may be, but is not limited to, a 1-bit flag. The information about whether to intrapredict using an extended reference line can be reported in units of a coding tree unit, a coding unit, or a prediction unit, or it can be reported in units of a sequence, a picture, or a segment. That is, whether to intrapredict using the extended baseline can be determined in units of a sequence, a picture, a slice, a CTU, a CU, or a PU.

Alternatively, whether or not to intrapredict using an extended reference line may be determined based on at least one of the current block size, shape, depth, or intraprediction modes.

When it is determined to perform intra-prediction using an extended reference line, a number of reference lines can be determined. Here, several reference lines may have a fixed value, and may be adaptively determined based on the size, shape, or intraprediction mode of a current block. For example, when an intra-prediction mode of a current block is a non-directional mode, the intra-prediction of the current block is performed using a reference line. When an intra-prediction mode of a current block is a directional mode, the intra-prediction of the current block can be performed using a plurality of reference lines.

For a further example, a number of reference lines can be determined by the information that is indicated in units of a sequence, an image, a slice or a unit to be decoded. Here, the unit to be decoded may represent a coding tree unit, a coding unit, a transformation unit, a prediction unit, or the like. For example, a syntax element 'max_intra_line_idx_minus2' indicating a number of available reference lines available in a sequence or a segment can be signaled via a sequence header or a segment header. In this case, the number of reference lines available can be set to max_intra_line_idx_minus2 2.

Next, a method for performing intra-forecasting using an extended baseline will be described in detail.

Fig. 16 is a flow chart illustrating a method for performing intra-prediction using an extended baseline in accordance with the present invention.

First, a decoder can generate a plurality of reference lines (S1610). The reference samples included in each reference line may be generated based on the reconstructed samples included in blocks decoded before a current block.

When an intra-prediction mode of a current block is a directional mode, a decoder may generate a reference line considering a directionality of the intra-prediction mode. Considering the directionality of an intra-prediction mode, a larger number of reference samples can be included in the k-th reference line than in the (k-1)-th reference line. That is, a reference line far from a current block may include a greater number of reference samples than a reference line near the current block.

Here, several reference samples included further in the k-th reference line than in the (k-1)-th reference line can be variably determined according to a size, a shape or an intra-prediction mode of a current block.

For example, when a current block has a size of 4x4, the k-th reference line may include four more reference samples (specifically, 2 in the horizontal direction and 2 in the vertical direction) than the reference line (k-1). -th. In addition, when a current block has a size of 8x8, the k-th reference line may further include eight reference samples (specifically, 4 in the horizontal direction and 4 in the vertical direction) than the reference line (k-1)- th

Referring to Fig. 15, since the size of a current block is 4x4, it is exemplified that a first reference line includes a total of 9 reference samples and a second reference line includes a total of 13 (= 9 2x2) samples. reference.

When a current block is not square, multiple reference samples included in a reference line can be determined according to the horizontal and vertical lengths of a current block.

For example, Fig. 17 is a diagram exemplifying a plurality of reference lines for a non-square block. Describing with Figures 15 and 17, as the width of a current block decreases to 1/2, a number of upper reference samples except one upper left reference sample included in a reference line 0 is reduced from 8 to 4. .

That is, according to Figures 15 and 17, when a current block is assumed to have size WxH, the kth reference line can include a total of 2{(W H)+ 2(k-1)}+1 samples. reference samples including W H 2(k-1) upper reference samples (or 2W 2(k-1) upper reference samples) (i.e., reference samples in the horizontal direction), W H 2(k-1) upper reference samples left reference (or 2H 2(k-1) left reference samples (ie, reference samples in vertical direction) and upper left reference sample.

If a reference sample that is not available is included in a reference line, the missing reference sample can be replaced with a nearby available reference sample. At this time, the neighboring sample that replaces the missing reference sample may be included in the same baseline as the missing reference sample, or may be included in a different baseline than the missing reference sample.

For example, if a reference sample position is outside of an image or in a different sector of a current block when intrapredicting using an extended reference line, or if a reference sample is included in an interprediction-encoded block when the intraprediction is made using an extended reference line, the sample of reference may be determined to be unavailable. The reference sample included in an interprediction coded block may be determined to be unavailable when a reference sample included in an interprediction coded block is set to be unused (eg only when the value of constraint_intra_prediction_flag is 0). Or, if it is established that an intraprediction coded block should be decoded before an interprediction coded block, the interprediction coded block still cannot be reconstructed when the intraprediction coded block is. Consequently, a reference sample included in the interprediction coded block may be determined to be unavailable.

A reference sample used to replace an unavailable reference sample may be determined by considering a position of the unavailable reference sample, a distance between the unavailable reference sample and the available reference sample, or the like. For example, a missing sample can be replaced with an available sample that is a shorter distance than the missing reference sample. That is, an available reference sample having the shortest distance and is selected by comparing a distance (first offset) between an available reference sample included on the same reference line with the unavailable reference sample and the unavailable sample and a distance (second offset) between an available reference sample included in a different reference line than the non-available reference sample and the non-available sample may be replaced by the non-available reference sample.

In the example shown in Fig. 18, a distance between the unavailable reference sample included in reference line 0 and the available reference sample included in reference line 0 is represented to be 4, and a distance between the reference sample The unavailable reference sample included in baseline 0 and the available The reference sample included in baseline 2 is 2. Therefore, the unavailable sample included in baseline 0 can be substituted using the available reference sample included in baseline 2.

If a first offset and a second offset are equal, a missing reference sample may be replaced by using an available reference sample included on the same reference line as the reference sample. reference not available.

An unavailable reference sample may be replaced using an available reference sample included on a different reference line from the unavailable reference sample only when there is a distance (i.e., a first offset) between an available sample included on the same line than the reference sample not available and the reference sample not available is equal to or greater than N. Alternatively, even when the first offset is equal to or greater than N, an available reference sample included in a reference line may be used. reference different from a reference unavailable sample to override the reference unavailable sample only when a second offset is smaller than the first offset. Here, N can represent an integer of 1 or more.

If a first offset is not equal to or greater than N, a missing reference sample may be replaced by using an available reference sample included on the same reference line as the missing reference sample.

Figures 19 and 20 show an example where an unavailable reference sample is replaced with an available reference sample when N is 2. If the distance between an unavailable reference sample included in reference line 0 and a reference sample available included in reference line 0 is 2, as in the example shown in Figure 19, the unavailable reference sample included in reference line 0 can be replaced using an available reference sample included in reference line 1.

On the other hand, if a distance between an unavailable reference sample included in reference line 0 and an available reference sample included in reference line 0 is 1, as in the example shown in Fig. 20, the unavailable reference sample included in baseline 0 can be replaced using the available reference sample included in baseline 0.

An unavailable reference sample may be replaced by using an available reference sample included in the same reference line as the unavailable reference sample or an available reference sample included in a reference line adjacent to a reference line on which includes reference sample not available. Here, a reference line adjacent to a reference line in which the missing reference sample is included may refer to a reference line that has an index difference of 1 from the reference line, including the unavailable reference sample. available. Alternatively, the missing reference sample may be replaced with an available reference sample included in a baseline that has an index difference of two or more from the baseline, including the missing reference sample.

Alternatively, an unavailable reference sample may be replaced by using an available reference sample included in a reference line that has a larger index value or has a smaller index value than a reference line that includes the unavailable reference sample. available. For example, if a reference line is used that has a higher index value than a reference line that includes the missing reference sample, a reference sample located to the left or top of the sample can be used. reference sample not available to replace the reference sample not available.

The search for an available reference sample to replace an unavailable reference sample can be performed in a predefined direction. For example, to replace the missing reference sample, only one reference sample located in the direction of a top, bottom, left, or right of the missing sample can be used among the reference samples included in the same reference line. than the reference sample not available. Alternatively, to replace the missing sample, only a reference sample located in a higher, lower, left, or right direction of the missing sample may be used among reference samples included in a different reference line from the reference sample. not available.

A decoder may decode, based on a bit stream, index information specifying one of a plurality of reference lines (S1620). For example, when there are 4 reference lines available as in the example shown in Figure 15, the index information can specify any of the 4 reference lines.

A baseline for performing intraprediction for a current block may be adaptively determined based on the size of a current block, a current block type, an intraprediction mode of a current block, index information in a neighboring block, or difference. between an intra-prediction mode of a current block and a predetermined intra-prediction mode, and the like.

When any one of a plurality of reference lines is determined, a decoder may perform an intra-prediction for a current block using the determined reference line (S1630).

For example, when an intra-prediction mode of a current block is DC mode, a prediction sample of the current block can be generated based on an average value (dcVal) of reference samples included in the determined reference line. Referring to Figs. 21 and 22, a calculation of the average value of the reference samples included in the reference line will be described in detail.

Alternatively, when an intra-prediction mode of a current block is a directional mode, a prediction sample of the current block may be generated based on a reference sample specified by the directional mode among the reference samples included in the determined reference line. At this time, if a line segment extending from a prediction sample to the direction indicated by the directional mode points between reference samples, the prediction sample of the current block can be generated based on a weighted sum (prediction weighted) of a first reference sample and a second reference sample lying on either side of the point indicated by the line segment extending in the direction indicated by the directional mode.

When an intra-prediction mode of a current block is DC mode, it is necessary to calculate an average value (dcVal) of reference samples included in a reference line to perform the prediction on the current block. At this time, the average value for the reference samples at the kth reference line can be calculated using only a part of the reference samples included in the kth reference line. At this time, the number of reference samples used to derive the average value may be the same for each reference line, or it may be different for each reference line. reference.

Alternatively, an average value for reference samples at the kth reference line can be derived using all reference samples included in the kth reference line. Alternatively, it can be determined based on the size of a current block, a shape of a current block or a position of a reference line to either derive an average value using a part of reference samples at the kth reference line or to derive an average value using all reference samples at the kth reference line.

Figure 21 is a diagram illustrating reference samples used to derive an average value from a reference line.

Fig. 21 shows an example of deriving a reference sample mean value of the kth reference line using a part of the reference samples included in a reference line. For example, an example illustrated in Figure 21, a reference sample average value of a first reference line adjacent to a current block (i.e. reference line 0 shown in Figure 21) can be calculated using top reference swatches and left reference swatches excluding a reference swatch adjacent to an upper left corner of the current block. That is, when a current block size is NxN, a total of 4N reference samples such as 2N upper reference samples and 2N left reference samples can be used for calculation of the average value of the first reference line.

The number of reference samples used to calculate a reference sample mean value of the kth reference line may be equal to the number of reference samples used to calculate the reference sample mean value of the first line of reference. At this time, a position of a reference sample used to calculate the average value of the kth reference line may correspond to a position of a reference sample used to calculate the average value of the reference sample of the first line. reference.

A reference sample on the kth reference line corresponding to a reference sample on a first reference line may have the same x-coordinate or the same y-coordinate as the reference sample of the first reference line. For example, a coordinate of an upper reference sample included in the kth reference line corresponding to an upper reference sample P(i, j) included in a first reference line may be P(i, jk 1) which has the same x coordinate as P(i, j). For example, a coordinate of a left reference sample at the kth reference line corresponding to a left reference sample P(i, j) included in a first reference line may be P(ik 1, j) which has the same and coordinate as P(i, j).

In Fig. 21, the reference samples of the second to fourth reference lines corresponding to the upper reference sample and the left reference sample are shown on a first reference line. A reference sample average value of each reference line can be calculated using the reference samples shown in Figure 21.

In Fig. 21, a current block is assumed to have a square shape, but even if the current block has a non-square shape, the above embodiment can be applied as it is. For example, when the current is a non-square block having size WxH, a reference sample average value of each reference line can be calculated using a total of 2(W H) reference samples, such as upper reference samples 2W and left reference samples 2H. Consequently, as in the example shown in Figure 22, the number of reference samples used to calculate an average value of the kth reference line can have the same value as the number of reference samples used to calculate a value average of the first reference line. In addition, the location of the reference sample used to calculate the mean value of the kth reference line may correspond to the location of the reference sample used to calculate the mean value of the reference sample of the first reference line. .

In figures 21 and 22, the top reference samples are used to double the width of a current block and for the left reference samples and twice the height of the current block to calculate the average value of a reference sample of a line reference. A reference sample average value of a reference line can be calculated using a smaller or larger number of reference samples than those shown in Figures 21 and Figure 22.

For example, the reference sample average value of the reference line can be calculated using the same number of top reference samples as the current block width and the same number of left reference samples as the current block height.

The average value of a reference sample from a reference line can be calculated by assigning different weights to the reference samples, depending on the shape of a current block and the position of a reference sample. For example, if the current block has a square shape, the average value of the reference sample can be calculated by assigning the same weight to the top reference samples and the left reference samples. On the other hand, when the current block has a non-square shape, the average value of the reference sample can be calculated by assigning a higher weight to one of the upper reference samples and the left reference samples. For example, if the height of the current block is greater than a width, the average value can be calculated by assigning a higher weight to the top reference samples than the left reference samples. On the other hand, when the width of the current block is greater than the height, the average value can be calculated by assigning a greater weight to the left reference samples than the upper reference samples.

For example, when the current block size is N/2 * N, the average value of the kth reference line dcVal can be calculated using the following Equation 12.

Equation 12

For example, when the current block size is NxN/2, the average value of the kth baseline dcVal can be calculated using the following Equation 13.

Equation 13

In equations 12 and 13, k can be set to a value between 1 and max_intra_line_idx_minus2 2 .

In the example described through Fig. 16, it is exemplified that index information specifying one of the plurality of reference lines is decoded after generating a plurality of reference lines. It is also possible to obtain only one reference line specified by the index information among a plurality of reference lines after decoding the index information specifying one of the plurality of reference lines.

In the embodiment described through Fig. 16, it is described that intra-prediction for a current block is performed using any reference line specified by index information among a plurality of reference lines. It is also possible that intra-prediction for a current block can be performed using two or more reference lines among a plurality of reference lines. Whether or not to use two or more reference lines to perform intra-prediction for a current block can be determined based on information signaled from a bit stream, a current block size, current block type, an intra-prediction mode of a current block, whether an intra-prediction mode of a current block is a non-directional one or a difference between an intra-prediction mode of a current block and a predetermined intra-prediction mode, and the like.

The two or more reference lines may be specified by a plurality of index information signaled from a bit stream. For example, when two reference lines are established to be used, either of the two reference lines may be specified by the first index information, and the other may be specified by the second index information.

Alternatively, two or more reference lines may be spatially contiguous. In this case, the index information to specify any of the two or more reference lines may be signaled via a bit stream. If any two or more reference lines are selected by the index information, the remaining reference line can be automatically selected in function of the spatial adjacency with the selected reference line. For example, when configured to use two reference lines, and the index information indicates 'reference line 0', then intraprediction of a current block can be performed based on reference line 0 and reference line 1 adjacent to reference line 0.

When configured to use a plurality of reference lines, intraprediction of a current block can be performed based on an average value, a maximum value, a minimum value, or a weighted sum of reference samples included in the plurality of reference lines. .

For example, assuming that an intra-prediction mode of a current block is a directional mode (i.e., an angular mode), a predicted sample of the current block can be generated based on a first reference sample and a second reference sample, each of which is included in a difference reference line. Here, a first reference line including the first reference sample and a second reference line including the second reference sample may be positioned next to each other, but are not limited to them. Furthermore, the first reference sample and the second reference sample can be determined by an intra-prediction mode of the current block. The first reference sample and the second reference sample can be placed close to each other, but are not limited to them. A prediction sample of a current block can be generated by considering the weighted sum of the first reference sample and the second reference sample, or it can be generated based on an average value, a minimum value, or a maximum value of the first sample. reference sample and the second reference sample.

The internal prediction of a current block can be performed by performing a first intra-prediction based on a part of a plurality of reference lines and performing a second intra-prediction based on the remaining reference lines. Here, an intra-prediction mode used in a first intra-prediction and an intra-prediction mode used in a second intra-prediction may be the same or different. A prediction sample of a current block may be generated based on a first prediction sample generated by performing a first intra-prediction and a second prediction sample generated by performing a second intra-prediction.

The above embodiments have been mainly described in the decoding process, the encoding process can be performed in the same order as described or in the reverse order.

Although the embodiments described above have been described on the basis of a series of steps or flowcharts, they do not limit the order of the time series of the invention, and can be performed simultaneously or in different orders as needed. Furthermore, each of the components (eg, units, modules, etc.) constituting the block diagram in the above-described embodiments may be implemented by a hardware or software device, and a plurality of components. Or a plurality of components can be combined and implemented by a single hardware or software device. The above-described embodiments can be implemented in the form of program instructions that can be executed through various computer components and recorded on a computer-readable recording medium. The computer readable recording medium may include one or a combination of program commands, data files, data structures, and the like. Examples of computer-readable media include magnetic media such as hard drives, diskettes, and magnetic tapes, optical recording media such as CD-ROMs and DVDs, magneto-optical media such as floppy disks, media, and hardware devices specifically configured to store and execute computer instructions. program, such as ROM, RAM, flash memory, etc. The hardware device may be configured to function as one or more software modules for performing the process according to the present invention, and vice versa.

industrial applicability

The present invention can be applied to electronic devices that can encode/decode a video.

Claims (10)

1. A method for decoding a video, the method comprises: determining a reference sample line for a current block based on a set of reference sample line candidates; perform intraprediction for the current block based on reference samples included in the reference sample line; and rebuild the current block based on prediction samples resulting from intra-prediction, where a number of reference sample line candidates in the reference sample line candidate set is determined based on signaled information at a sequence level, where, depending on the information, the reference sample line candidate set comprises only a first reference sample line adjacent to the current block, or comprises both the first reference sample line and a second reference sample line not adjacent to the current block, where when the set of reference sample line candidates comprises both the first reference sample line and the second reference sample line, the second reference sample line not adjacent to the current block is not used as the sample line current block reference when a default intraprediction mode is applied to the current block, the default intraprediction mode comprises a Planar mode but not a DC mode, and wherein if an intra-prediction mode of the current block is the DC mode, a prediction sample of the current block is obtained based on a DC value obtained based on the reference samples included in the reference sample line of the current block. The method of claim 1, wherein the reference sample line for the current block is determined based on indexed information by specifying one of the reference sample line candidates. The method of claim 1, wherein the reference samples comprise upper reference samples and left reference samples, and in which whether to use both the upper reference samples and the lower reference samples reference samples or using a part of the upper reference samples and the left reference samples to obtain the DC value, is determined based on a shape of the current block. The method of claim 3, wherein a number of the upper reference samples used to obtain the DC value is identical to a width of the current block. The method of claim 3, wherein a number of the left reference samples used to obtain the DC value is identical to a height of the current block. The method of claim 1, wherein the reference samples comprise top reference samples and left reference samples, where the DC value is obtained by a weighted sum of the upper reference samples and the left reference samples, and where a first weight applied to the upper reference samples and a second weight applied to the left reference samples are determined based on a shape of the current block. 7. A method of encoding a video, the method comprising: determining a reference sample line for a current block among a set of reference sample line candidates; perform intraprediction for the current block based on reference samples included in the reference sample line; and obtain residual samples by subtracting prediction samples resulting from the intraprediction of original samples, wherein the information used to determine a number of reference sample line candidates in the reference sample line candidate set is encoded at a sequence level, where the reference sample line candidate set comprises only a first reference sample line adjacent to the current block, or comprises both the first reference sample line and a second reference sample line not adjacent to the current block, where when the set of reference sample line candidates comprises both the first reference sample line and the second reference sample line, the non-adjacent second reference sample line to the current block is not used as the reference sample line of the current block when a default intraprediction mode is applied to the current block, the default intraprediction mode comprises a Planar mode but not a DC mode, and wherein if an intra-prediction mode of the current block is the DC mode, a prediction sample of the current block is obtained based on a DC value of the reference samples included in the reference sample line of the current block. The method of claim 7, wherein the index information specifying one of the reference sample line candidates is encoded in a bit stream. The method of claim 7, wherein the reference samples comprise top reference samples and left reference samples, and wherein whether to use both the upper reference samples and the left reference samples to obtain the DC value or to use a part of the upper reference samples and the left reference samples to obtain the DCo value is determined based on a form of the current block. The method of claim 7, wherein the reference samples comprise top reference samples and left reference samples, and where the DC value is obtained by a weighted sum of the upper reference samples and the left reference samples, and where a first weight applied to the upper reference samples and a second weight applied to the left reference samples are determined based on a shape of the current block.